Caltrans outlines five-year plan for Ferguson rock shed to restore SR-140
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Summary
Caltrans engineers presented an updated design and schedule for a segmentally launched rock shed to permanently reopen State Route 140 through the Merced River Canyon. The agency said construction could take about five years and will require major materials, special heavy-moving equipment and state funding approval this spring.
Caltrans on Tuesday told the Mariposa County Board of Supervisors it plans to build a segmentally launched rock shed to restore full access to State Route 140 after the 2006 rockslide that buried the highway.
The rock shed will be anchored into the mountainside and assembled from precast concrete ‘‘boxes’’ that will be jacked into place. ‘‘The purpose of our project is to restore full access to State Route 140,’’ Caltrans project manager Corey Casey told the board, adding the structure must be anchored with multiple high-capacity rock anchors because of ongoing slope movement.
The agency abandoned earlier bridge and tunnel concepts after environmental review and geological study. A tunnel option would have required a 1.2-mile bore with complex ventilation and safety systems and would likely have cost far more than the preferred rock shed, Casey said. He described a revised construction method following a 2015 rockfall that required deeper geotechnical investigation and design changes.
Caltrans described a plan to build foundations and vertical piles in the hillside, then assemble 11 precast segments and move them into position with specialized heavy-moving equipment. ‘‘Each [anchor] is rated for 1,200,000 pounds,’’ Casey said. He told the board the work will require roughly 36,000 cubic yards of concrete and about 20,000,000 pounds of rebar and will be constructed in a confined, highly regulated canyon environment.
The project team plans to seek construction funding from the California Transportation Commission in May and to negotiate a contract with a preselected contractor this summer; Casey said the agency hopes to begin onsite work the same year and estimated about five years of construction, weather permitting. He also said Caltrans will hold community open houses in April in El Portal, Midpines and Mariposa to present details and answer questions.
Supervisor questions focused on staging areas, truck and material logistics, and whether onsite batching would be used. Caltrans said it expects to place a portable batch plant in the sand area between El Portal and the slide site and to coordinate truck traffic and work schedules to reduce disruption. The agency said it is working with a European heavy-moving firm experienced in shifting large structural segments.
The board and audience members asked about schedule risk and funding. Casey said the estimate near $300 million is ‘‘hefty’’ but that the rock shed is the least-cost feasible permanent solution; he said a tunnel would likely exceed a billion dollars. The project is being advanced as an emergency reconstruction project with federal and state reimbursement, but it competes for funding among other state emergencies, he said.
The board requested continued updates and welcomed the planned public outreach. Caltrans noted tribal and environmental constraints were key factors in choosing a rock-shed solution rather than a bridge and said specialists had been engaged throughout design and geotechnical work.
Ending: Caltrans will return with more detailed schedules and public outreach dates; the county expects spring open houses and a funding request before the California Transportation Commission in May.
